How to Make It
Light a grill or preheat a large cast-iron grill pan. In a medium bowl, toss the lamb with 1 tablespoon of the olive oil and season with salt and pepper. Alternate the lamb on four 12-inch skewers with pieces of red onion.
In another bowl, combine the garlic with the balsamic vinegar and 3 tablespoons of the olive oil. Add the tomatoes and basil, season with salt and pepper and toss well.
Brush the bread on both sides with the remaining 1 tablespoon of oil. Grill, turning once, until toasted, about 2 minutes per side. Spread about 2 teaspoons of the tapenade on each toast. Grill the lamb until browned all over, 7 to 8 minutes for medium rare meat. Spread the remaining tapenade on the lamb.
Spoon the tomato salad onto large plates. Add a lamb skewer and a tapenade toast to each and serve.